Poor service from manager/price error

I visited Builders Express at N1 City on 14 February 2025. I was shopping around for a drill and was not initially going to buy one on the day however I was assisted by a sales assistant who was very helpful. He then showed me a drill that was perfect for what I needed and that was on promotion for R329.50 from R550 which is a good bargain. I decided to buy the drill, however the price at the checkout scanned R499 and I explained to the cashier that the sales assistant showed me the price on the display which showed “was R550, Now R329.50. She then got the price tag and confirmed it is for the item I was purchasing. The manager on duty then tried to override the price but it didn’t allow her to. She then very rudely said there’s nothing she can do I have to either pay R500 or leave it and she then walked away. I would like to know how a manager can speak to a customer like that and how are products being displayed with marked down prices and customers not being able to pay the marked down price?